The majority of presently used photographic processes utilize substrates which have been precoated with one or more light sensitive substances and which usually contain silver compounds in a gelatin or other suitable base (emulsion). Such coatings may also include colored dyes and/or other substances which impart other desirable properties to a PSM in addition to light sensitivity. PSM may be produced to be sensitive to (record) only a very narrow spectral (light) range or it may be designed to be sensitive to a wide spectral range or even several different ranges simultaneously, depending on the particular characteristics desired in the finished product.
Regardless of the spectral range a particular PSM is designed to record, the vast majority require liquid chemical processing after being exposed before the pattern (the latent image) of light recorded on the PSM can be seen (as in a photographic negative or print) or utilized for other purposes (as in an offset printing plate). Such processing usually takes the form of wetting the PSM with one or more chemicals which react with the light sensitive compounds contained within the coating(s) on the PSM substrate. The exact number of chemicals, their exact characteristics and the number of processing steps required to fully process a particular PSM depends on the desired characteristics the particular PSM is designed to exhibit.
For example: In the case of a color transparency PSM (slide) such characteristics usually include the accurate rendition of the colors and light patterns in a scene photographed with a camera, and it could require as many as thirteen (13) individual processing steps to produce a finished slide; or, as in the case of a photographically produced offset printing plate, such characteristics usually include the ability to create an ink receptive surface (printing area) in certain areas of the plate's surface while creating a water receptive surface (non-printing area) in other areas, and it may only require one or two processing steps to complete.
Processing silver-based PSM typically involves immersing the exposed material in a developer solution which reacts to varying degrees with the silver compounds contained in the PSM, depending on the amount of light which struck them. Unwanted by-products and/or unused compounds are then removed in further processing steps and most PSM are then either washed with water to remove any remaining chemical residue or stabilized chemically and then dried.
Many commonly used batch type (non replenished) photo processing solutions have a short useful life; from just a few hours up to several days. They either become exhausted by the amount of PSM processed in them, or they may oxidize or undergo some other change in which renders them unfit for further use.
Many larger commercial processing operations use processing solutions which may last many months but which must constantly be replenished with chemicals to replace those exhausted by the chemical reactions taking place during processing or to compensate for oxidation or other changing conditions. If the delicate chemical balance required goes beyond allowable tolerances the entire batch must be discarded.
Most processing methods necessitate exposing the processing solutions to ambient atmospheric conditions causing detrimental effects which adversely affect the quality of the final result and/or the useful life of a processing solution. This is commonly referred to in the industry as aerial oxidation (Note: this term is not always technically correct since some effects are not actually oxygen related). Conversely, due to the nature of certain processing solutions, fumes given off by them may have an adverse effect on the surrounding environment. The present invention offers a method of photographic processing which minimizes the amount of atmospheric interaction possible between the processing solutions and the surrounding environment thus tending to optimize the useful life of such solutions.
With regards to the quality of end results and processing overall time required to achieve satisfactory results the majority of PSM respond directly to manipulation of three well known major factors: (1) the temperature of the processing solution that the PSM is exposed to, (2) the amount of time the PSM is exposed to a processing solution, and (3) the amount (and eveness) of the agitation occurring while the PSM is exposed to the processing solution.
Temperature is a major factor because it directly relates to the chemical activity of the processing solution. Time is a major factor since it relates to how long a PSM is exposed to the chemical activity of a processing solution. Agitation is a particularly important factor since it facilitates the removal of reaction by-products and depleted solution from the surface of the PSM emulsion and allows for the continuous introduction of fresh processing solution.
Agitation is considered by many industry experts to have the greatest overall effect since it tends to increase the availability of the solution required for adequate processing and/or assists in removing processing by-products (some of which may actually retard chemical reactions). Both time and temperature factors may be affected advantageously. If agitation is absent, inadequate, or uneven, the chemical activity taking place in the emulsion of a PSM during processing may vary and the final results may be inconsistent and unacceptable. Among other desirable features the present invention offers an economical, simple and yet highly efficient method for optimizing the positive effects of agitation.
Regardless of the means employed in initially exposing the PSM to develop the latent image thereon, it is recognized in the art that subsequent processing of the PSM to develop the image is critical to the successful attainment of the desired print. The PSM processing methods and apparatus known in the art are too numerous to set forth herein, but are well understood to seek to ensure faithful repetition of the selected process parameters. These known systems, however, suffer from such undesirable features as excessive liquid processing substances such as commonly used to ensure full and complete contact between the PSM and the process substance, complex PSM transport apparatus intended to prevent physical damage to the PSM processing while still ensuring that the portion of the PSM that bears the latent image is fully exposed to active process substance, and often, large and/or cumbersome mechanical requirements. Certain prior processing and transporting systems also suffer disadvantages relating to initial cost, operating costs, speed of processing, etc.
Most presently known devices for transporting, positioning and processing sheets of exposed photosensitive materials employ a system of rollers or vacuum belts that convey the PSM into a processor which has one or more containers filled with liquid chemical processing mixtures. Other methods employ gels of chemical mixtures which are applied to a dry photosensitive material by means of a system of rollers (such as in a Polaroid camera). Still others employ means by which dry PSM is transported and processed by threading long rolls of the PSM through appropriate apparatus and winding it up on the end of a take-up spool (such as is done with movie films).
The mechanical complexity of all of the above methods is largely dependent on the size range of materials being handled, and the number of chemical steps involved, i.e. a processor designed to handle film sizes ranging from 4".times.5" to 20".times.24" with a system of rollers would require a minimum width of 20" but roller pairs could not be more than 5" apart or the smallest sheets could not be transported. Continuous systems like movie processors generally handle only certain discrete sizes, usually under 70 mm in width.
Regardless of whether the PSM is color, or black and white, all of the PSM covered by the present invention function by the well known effects caused by some form of radiation (i.e. light) striking a "photosensitive" silver compound which has been coated onto a substrate.